Familial manic-depressive illness with deleted short arm of chromosome 21: coincidental or causal?

Inv21p12q22del21q22 and intellectual disability

Chromosomal rearrangements are common in humans. Pericentric inversions are among the most frequent aberrations (1-2%). Most inversions are balanced and do not cause problems in carriers unless one of the breakpoints disrupts important functional genes, has near submicroscopic copy number variants or hosts "cryptic" complex chromosomal rearrangements. Pericentric inversions can lead to imbalance in offspring. Less than 3% of Down syndrome patients have duplication as a result of parental pericentric inversion of chromosome 21. We report a family with an apparently balanced pericentric inversion of chromosome 21. The proband, a 23-year-old female was referred for prenatal diagnosis at 16 weeks gestation because of increased nuchal translucency. She has a familial history of Down's syndrome and moderate intellectual disability, a personal history of four spontaneous abortions and learning difficulties. Peripheral blood and amniotic fluid samples were collected to perform proband's and fetus' cytogenetic analyses. Additionally, another six family members were evaluated and cytogenetic analysis was performed. Complementary FISH and MLPA studies were carried out. An apparent balanced chromosome 21 pericentric inversion was observed in four family members, two revealed a recombinant chromosome 21 with partial trisomy, and one a full trisomy 21 with an inverted chromosome 21. Array CGH analysis was performed in the mother and the brother's proband. MLPA and aCGH studies identified a deletion of about 1.7 Mb on the long arm of inverted chromosome 21q22.11. We believe the cause of the intellectual disability/learning difficulties observed in the members with the inversion is related to this deletion. The recombinant chromosome 21 has a partial trisomy including the DSCR with no deletion. The risk for carriers of having a child with multiple malformations/intellectual disability is about 30% depending on whether and how this rearrangement interferes with meiosis.

Chromosomal abnormalities and mental illness

Linkage studies of mental illness have provided suggestive evidence of susceptibility loci over many broad chromosomal regions. Pinpointing causative gene mutations by conventional linkage strategies alone is problematic. The breakpoints of chromosomal abnormalities occurring in patients with mental illness may be more direct pointers to the relevant gene locus. Publications that describe patients where chromosomal abnormalities co-exist with mental illness are reviewed along with supporting evidence that this may amount to an association. Chromosomal abnormalities are considered to be of possible significance if (a) the abnormality is rare and there are independent reports of its coexistence with psychiatric illness, or (b) there is colocalisation of the abnormality with a region of suggestive linkage findings, or (c) there is an apparent cosegregation of the abnormality with psychiatric illness within the individual's family. Breakpoints have been described within many of the loci suggested by linkage studies and these findings support the hypothesis that shared susceptibility factors for schizophrenia and bipolar disorder may exist. If these abnormalities directly disrupt coding regions, then combining molecular genetic breakpoint cloning with bioinformatic sequence analysis may be a method of rapidly identifying candidate genes. Full karyotyping of individuals with psychotic illness especially where this coexists with mild learning disability, dysmorphism or a strong family history of mental disorder is encouraged.

A cytogenetic study of Kuwaiti couples with infertility and reproductive disorders: short arm deletion of chromosome 21 is associated with male infertility

Chromosomal anomalies may be a reason for both male and female infertility. The aim of this study was to investigate the contribution of chromosomal abnormalities in sterile couples from Kuwait. A total of 118 patients with clinical diagnosis of infertility was analyzed using cytogenetic banding techniques. Common chromosomal abnormalities were detected in 12 patients. We describe here one new case of an infertile male with the karyotype 46,XY, del(21)(pter;q11.2). The overall incidence of 11% abnormality indicates that routine chromosome analysis of infertile couples in Kuwait should be considered before the planning of intracytoplasmic sperm injection.

Linkage study between manic-depressive illness and chromosome 21

Chromosome 21, of interest as potentially containing a disease gene for manic-depressive illness as possible evidence for a gene pre-disposing to affective disorder, has recently been reported in a single large family as well as samples of families. The present study investigates for linkage between manic-depressive illness and markers covering the long arm of chromosome 21 in two manic-depressive families, using ten microsatellite polymorphisms as markers. No conclusive evidence for a disease gene on the long arm of chromosome 21 was found. Assuming either a dominant or recessive mode of inheritance, close linkage to the marker PFKL, which has been reported as possibly linked to affective disorder, seems unlikely in the families studied here. PFKL and more telomeric markers yielded small positive lod scores at higher recombination fractions in the largest family, and small positive lod scores at lower recombination fractions in the affected-only analyses in the smallest family.

Systematic chromosome examination of two families with schizophrenia and two families with manic depressive illness

Systematic and detailed chromosome analysis, combined with a semistructured interview, was performed in 2 families with schizophrenia and in 2 families with manic depressive illness. Prometaphase technique did not reveal any subtle structural chromosome abnormalities. However, in standard techniques, gain and loss of sex chromosomes were observed. This occurred in patients at a younger age than in unaffected persons. This gives rise to the suspicion that sex chromosome aneuploidy may somehow be related to the development of psychosis. But since the data set is small, especially with respect to schizophrenia, further studies are needed to elucidate this observation. In one family, cosegregation of the disease locus with a marker on chromosome 21 was seen. Therefore, further research should determine if chromosome 21 contains a gene for manic depressive illness.

Is there an inverse relationship between Down's syndrome and bipolar affective disorder? Literature review and genetic implications

Several authors have suggested the existence of an inverse relationship between bipolar affective disorder and Down's syndrome (DS). The present authors have examined this hypothesis by a critical review of the literature. The present findings are consistent with a reduced rate of bipolar disorder in subjects with DS when compared with non-DS mentally retarded adults and with the general population. Thus, possession of an extra copy of chromosome 21 may confer protection against bipolar disorder. This could be the result of non-specific mechanisms or the action of a disease-modifying gene. However, the most interesting possibility is that either dominant or recessive alleles act at a major susceptibility locus for bipolar disorder on chromosome 21. Testable predictions result from the major susceptibility locus models. In order to investigate these hypotheses further, the present authors suggest the following: (1) further studies of the prevalence of bipolar disorder in DS; and (2) the reporting of all cases of bipolar disorder in trisomy 21 with details of the meiotic origin of the non-disjunction and details about affective disorder in relatives of the proband.

Chromosomal aberrations and bipolar affective disorder

Chromosomal abnormalities associated with bipolar disorder may help in the localisation of susceptibility genes for bipolar illness by pinpointing 'candidate' regions of the genome for further study using molecular genetic methods. We review descriptions of chromosomal abnormalities in association with bipolar and related affective disorders and evaluate their relevance for localising susceptibility genes for bipolar disorder, using standardised criteria. We found 28 reports. We identified four genomic regions of potential interest: 11q21-25; 15q11-13; chromosome 21;Xq28. It is important that clinicians are able to recognise patients who may have chromosome abnormalities which could help in the localisation of susceptibility genes for psychiatric disorders. We suggest referral for specialist investigation and karyotyping, to a psychiatric genetics research group, of any patient with functional psychosis and one or more of the following: (a) a strong family history of functional psychosis; (b) mental retardation; (c) another disease known to be caused by a single gene; or (d) congenital abnormalities.

The genetics of bipolar disorder

Growing interest in the application of molecular biological techniques to psychiatric disorders has reinvigorated interest in the genetics of the psychoses. It is therefore timely to review the current state of knowledge of the genetics of bipolar disorder. Family, twin and adoption studies are all consistent in confirming the strongly heritable nature of this condition. As segregation analyses have been unable to determine the mode of transmission of bipolar disorder, ongoing linkage analyses using DNA markers will be crucial in determining whether this condition is due to a single major gene, a small number of genes, or multifactorial polygenic inheritance.

Chromosomal aberrations and schizophrenia. Autosomes

Chromosomal aberrations associated with schizophrenic disorders may suggest regions in which to focus a search for genes predisposing to schizophrenia by a linkage strategy. As for other genetic illnesses, chromosomal abnormalities may also provide useful tools for subsequent physical mapping, fine localisation, and isolation of important susceptibility genes. Identification of several chromosomal aberrations may be especially important, given the unknown pathophysiology, the paucity of known brain genes, and the probable genetic heterogeneity of schizophrenia and manic-depression. However, because psychiatric disorders are common and inherited in a complex manner, researchers must use caution when drawing inferences about associations with chromosomal aberrations. Reported abnormalities involving autosomes (chromosomes 1-22) associated with psychotic disorders are reviewed. Their relevance to linkage studies localising genes for schizophrenia was estimated by standardised criteria for specificity, diagnosis, family history, and overall weight of evidence. Four 'possibly relevant' chromosomal regions were identified: 5q, 11q, 18q, and 19p. This paper outlines strategies for future studies to detect new chromosomal aberrations associated with major psychotic disorders that may be relevant to isolating the genes for schizophrenia.